An integrated circuit (IC) is a device, which includes a plurality of electronic components (e.g. transistors, resistors, capacitors, etc.). These components are interconnected to form multiple circuit components (gates, cells, memory units, etc.) on the IC. Modern very large scale integration (VLSI) integrated circuits are typically made up of a power/ground (P/G) grid with a layer structure having multiple layers of wiring (called “metal layers”) that interconnect its electronic and circuit components. Each metal layer typically has a general wiring direction (e.g., a majority of the traces in the metal layer share the same direction, running substantially parallel to one another), and this general direction alternates between successive metal layers. Many IC designs use the Manhattan wiring model, where in each metal layer, all supplies to the IC's electronic and circuit components (e.g., global power supply and global ground) are laid out in a grid of parallel x-oriented or parallel y-oriented strips, and the components connect to these strips. Designs with multiple metal layers exhibit alternating layers of generally x-oriented and generally y-oriented wiring. In a multi-layer design, electrical interconnects (vias) between the metal layers allow the IC's components to be connected to the power and ground strips and to each other, thus completing the circuit.
To synchronize data transfer between the electrical components of the IC, clock signals may be generated by a clock signal generator and provided to the IC through clock pins. Clock signals are periodic signals alternating in amplitude between binary 0 and 1 (logical high and low). After receiving the clock signals from an external source (e.g., clock signal generator external to the IC), one or more of the metal layers in the P/G grid carry current to power the electrical components of the IC that drive or receive the clock signals.
An important aspect of IC design includes ensuring signal integrity, especially with changes in process, voltage, and temperature (PVT). For example, if the wire resistance and/or cell current of some cells within the IC exceeds a predetermined limit, voltage drops (also referred to as “IR drops” based on the voltage being equal to the current (I) multiplied by the resistance (R)) may occur, causing an increase in gate and signal delays and, in the worst case, switching failures of the integrated circuit. Thus, in order to avoid failures caused by signal integrity problems, sufficient electrical power should be provided to the cells within the integrated circuit.
In some cases, the IC may be constructed with small channel ultra-low-threshold-voltage implanted devices. In such cases, considerable power may be consumed to compensate for the voltage drop (IR drop) associated with the clock signal path of the small channel device. As a result, the peak-to-peak eye of the clock signal is significantly reduced for lower power (e.g., 825 mV) and high-speed applications.